1. Technical Field
This disclosure relates to computer networking. More specifically, this disclosure relates to systems and techniques for delivering congestion notifications in a network involving more than one layer-2 domain.
2. Related Art
Congestion notification (CN) has proved to be a useful tool for congestion management of long-lived data flows within network domains such as data centers, backplane fabrics, computing clusters, and storage networks. According to IEEE standard 802.1Qau (available at http://standards.ieee.org/about/get/802/802.1.html), the congestion notification (CN) mechanism can detect and mitigate queue congestions for selected classes of traffic in virtual bridged LANs by enabling bridges to signal congestion to end stations to avoid frame loss. In a CN-enabled network, when a switch detects congestion, the switch selects a frame from the congested queue and sends a congestion notification message (CNM) to the source of the selected frame. In response to the CNM, the source (also called a reaction point (RP)) decreases its transmission rate.
However, congestion notification is an end-to-end solution designed to operate within a single layer-2 domain, which means it terminates at devices that remove/replace source and/or destination media access control (MAC) headers. In a network that includes devices operating above layer 2, such as Internet Protocol (IP) routers or Fibre Channel Forwarders (FCFs), the CNMs will not be able to reach end stations at the other side of such devices. As a result, congestion notification as defined by the IEEE 802.1Qau standard cannot work in a network that includes multiple layer-2 domains, such as a Fibre Channel over Ethernet (FCoE) network.